The present invention relates to devices for obtaining continuous core samples for use in environmental research and analysis and other purposes and, more particularly, to a surface effect drilling craft for, among other uses, recovering such core samples from inaccessible environmentally sensitive, shallow wetlands.
Obtaining continuous core samples at strategic locations is essential to modern estuary and shallow lake margin studies. For this purpose, rotary coring tools, gravity or piston cores, and vibracore tools have been mounted on barges, pontoon boats and other displacement craft. The access of such a craft or vessel to intertidal zones is limited by the draft of the vessel and the timing of the tidal cycle. Coring tools have also been mounted on wheeled or tracked vehicles but such platforms cannot traverse roadless wetlands without damaging the ecosystem or its substrate. As a result of this, the very environments that receive and store modern sediments are inaccessible to research that depends on vertical sampling to provide the history of, and further data regarding, nutrient, sediment and contaminant flux from the land into ponds and estuaries. Moreover, conventional coring technology presents additional limitations for work in the wetlands. Rotary coring uses fluids and additives, and produces large amounts of cuttings that can contaminate the ecosystem. Gravity or piston coring devices and small vibracore tools are limited by materials that can impede penetration making it impossible, as a practical matter, to sample entire stratigraphic intervals that have been targeted for research.
In accordance with the invention, a surface effect drilling craft is provided which, among other uses, enables recovery of continuous core samples in normally inaccessible, environmentally sensitive areas. The surface effect craft or hovercraft can negotiate shallow water, mud flats, marshes, beaches and firm ground without tracking or damaging the ecosystem. In a preferred embodiment, a multi-sonic drill is mounted on the hovercraft and such a drill can penetrate and recover cores up to 30 meters in length, through materials of variable resistance, without the use of fluids No cuttings are produced and the environment around the drill site is not otherwise defiled or polluted. The cores provide the data necessary to document the history of the ecosystem in changing environments that have been previously inaccessible.
In accordance with the invention, a surface effect drilling craft is provided comprising: a hovercraft including an inner hull floor and a bottom hull disposed beneath the inner hull; a base mounting plate secured to the inner hull floor; a drill tube having an upper end and a lower end and extending through the base mounting plate, inner hull floor and bottom hull; a drill cap for, in use, closing off the drill tube during maneuvering of the hovercraft; and a drill rig mounted on the base mounting plate adjacent to the drill tube, the drill rig including a fixed lower section, and a pivotable upper section movable between an erected, operative position and a collapsed, inoperative position.
Preferably, as indicated above, the drill rig includes a multi-sonic drill for, e.g., taking continuous core samples. As set forth hereinbefore, a multi-sonic drill provides important advantages over other drilling devices.
The hovercraft has a balance point and the drill tube is located at the balance point to assist in providing proper trim. Advantageously, the drill rig is located on the hovercraft forward of the drill tube.
A support member is preferably provided for supporting the upper section of the drill rig in the inoperative position of the latter. The support member advantageously comprises a support crutch located on the hovercraft forward of the drill tube.
The hovercraft includes a buoyancy wall having an upper end and the upper end of the drill tube is preferably located below the upper end of said buoyancy wall.
Preferably, a special support means is provided for supporting the inner hull floor. Advantageously, the support means includes a plurality of vertical support elements extending between the inner hull floor and the bottom hull. The support elements preferably comprise stringers affixed to the bottom hull and connected by support angles to the inner hull floor.
More generally, support angles are preferably connected to the inner hull floor to provide strengthening thereof. The support angles are advantageously connected to the inner hull floor by bolts which also secure the base mounting plate in place.
Preferably, the hovercraft further comprises sealing means for providing an air and water seal between the drill tube and the bottom hull. The sealing means advantageously comprises a fiberglass resin seal.
Preferably, the hovercraft further comprises sealing means for providing an air seal between the drill tube and the inner hull floor. Advantageously, the air sealing means comprises a rubber seal.
Advantageously, the lower end of the drill tube projects below the bottom hull, and the hovercraft further comprises a protective member secured to the bottom hull for protecting the lower end of the drill tube from impact.
Further features and advantages of the present invention will be set forth in, or apparent from, the detailed description of preferred embodiments thereof which follows.